Where, in an apparatus of any kind, an element of the apparatus having a major function has to be adjusted by a professional, it is desirable to prevent any subsequent interference with the adjustment by an unauthorised entity, at least without it being evident that such tampering has taken place.
In particular, a motor vehicle headlight calls for horizontal optical adjustment (that is to say adjustment in azimuth), in particular to avoid dazzling of the drivers of vehicles travelling in the opposite direction. This adjustment is carried out in the factory by the manufacturer, after the headlight has been fitted in the vehicle. The position of the optical beam is adjusted as a function of inaccuracies in the manufacture of the body of the vehicle.
In order to prevent unauthorised modification of the adjustment, it has in the past been proposed to put in place, on the head of the control member, an anti-removal cover which is engaged in a direction parallel to the geometric axis of rotation of the control member. Fitting of this cover is quite a delicate operation, because access to the head of the control member is generally difficult. Fitting the anti-removal cover in place takes some time, and has to be carried out on the production line of the vehicle. In addition, in some adjusting devices for headlights, a central rod or rod element projects towards the rear from the support and enables the adjustment to be modified. The anti-removal cover that covers the adjusting head does not prevent unauthorised action on this central rod element.